Please enable JavaScript.
Coggle requires JavaScript to display documents.
3.1.5 - Mechanical devices - Coggle Diagram
3.1.5 - Mechanical devices
Types of motions
Linear
- straight line. e.g. train moves down a track
Rotary
- moving around an axis or a point. e.g. a wheel
Reciprocating
- repeated up & down, back & forth motion. e.g. a pump
Oscillating
- a curved back and forth movement that swings on a point. e.g. a swing
Changing magnitude and direction of force
Levers
make lifting or moving something much easier.
First lever
- Load and effort are on opposite sides on the fulcrum. e.g. Seesaw
Second order
- Fulcrum and effort on opposite side and load in between them. e.g. wheelbarrow
Third order
- Fulcrum at one end, load at the opposite end and the effort is applied in the middle somewhere.
Linkages
- a mechanism made by connecting rigid parts. It can change the magnitude & direction of a force or transform into a different motion.
Bell cranks
- the direction of the input movement or force would be turned through 90° at the output.
Uses - Brake calipers on bicycles. The force from the handlebar lever is turned 90° to squeeze the brake block.
Parallel motion or push/pull
use to fixed pivots - make the input & output travel in the same direction through a link arm.
Uses - tool boxes, sewing boxes which open up to reveal several layers.
Rotary systems
Cams
, usually circular. Uses an off-centre pivot to cause the pivot to move up & down.
uses - sewing machiens.
Simple Gear trains
-are when two or more gears are joined together. The drive gear causes the driven gear to turn the opposite direction.
Calculation for Gear ratio = 60/30 = 2
Gear ratio = 1:2
Belt
drives transfer movement from one rotating pulley to another. Generally made from soft, flexible material i.e. rubber. Grooves (perpendicular holes) on a pulley and belts help them grip and turn.
A driven pulley of 120mm is attached with a driver pulley of 40mm with a speed of 100rpm. What is the
velocity ratio?
Velocity ratio = diameter of the driven pulley ÷ diameter of the driver pulley.
120/40 = 3 = 3:1
Output speed?
Output speed = input speed (revolution per minute) ÷ velocity ratio
Output speed = 100rpm/3
= 33.3
Pulley
- wheel-shaped, allows cord though.
Use - move large objects, portable.
One pulley does not make a mechanical advantage because the same force is needed.
Several pulleys together create a mechanical advantage. e.g. two pulley = half the force to lift.
This is called a
block and tackle
and is used to lift heavy things
Followers
- the follower moves up and down through the movement of the CAM.
Roller
- have a circular ball sitting on the cam. They are accurate, low friction, can withstand load, more expensive
Flat
- flat bottom that sits on the cam. They cope well under load but aren't very accurate and have a lot of friction.
Knife/pointy
- Triangular point sits on cam. They are very accurate, low friction but the pointy edge wears off quickly.
